MSM7557 데이터 시트보기 (PDF) - Oki Electric Industry

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MSM7557

Single Chip MSK Modem with Compandor for Cordless Telephone

Oki Electric Industry 

¡ Semiconductor

MSM7557

(Continued)

Name

Modulator output level control.

Refer to the following figure.

From modulator

VR1

VR2

To transmit filter

VR3

Description

R1 ≥ 40 kW

R2 ≥ 40 kW

–

VR1

R1 ≥ R2

+

R1

VR2

R2

VR3

VTAO = 20 ¥ log (R2/R1) – 9 dBV (DYN = "0" )

VTAO = 20 ¥ log (R2/R1) – 1 dBV (DYN = "1" )

This level is made from internal voltage reference, so this level doesn't depend on power supply voltage.

Transmit side RC active filter input (TVI) and output (TVIO).

If over 50 kHz frequency element is in the input signal, folding noise is generated from internal SCF

circuit, so second order RC-active filter is needed. (fc = 10 kHz)

TVIO

TVI

C1 R3

C2

C19

R5

C3

R4

CMPI

TVIO

TVI –

+

SG

Compressor

R5 ≥ 60 kW

C1 and C19 are used for DC cut.

VTVI

Example of fc = 10 kHz and 0 dB gain

R3 = R4 = R5 = 68 kW

C1 = 0.22 mF, C2 = 510 pF, C3 = 110 pF

CC1

CC2

CC3N

CC3P

When digital "1" is applied to TVE pin, transmit voice signal comes out to TAO.

Capacitor connection pins to remove for DC offset of the compressor.

A 1 mF capacitor between SG pin and each pin should be connected.

Capacitor connection pins for the compressor attack and recovery time.

When DYN is digital "0" level, a 0.22 mF capacitor should be connected between CC3N and CC3P.

And when DYN is digital "1" level, a 0.47 mF capacitor should be connected between them.

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